Extrusion process

ABSTRACT

A process and apparatus for extruding feedstock in which the gripping force for extrusion of the feedstock is derived by forcing the feedstock into a passageway to develop in the feedstock on two opposing surfaces a pressure of at least the yield strength of the feedstock and moving the opposed walls of the passageway toward an end wall with extrusion orifice means located at or near the end wall of the passageway where additional constraining walls are provided at least as long as the upset length of the feedstock so as to restrain the same within the passageway, the engagement of the feedstock between the moving walls creating sufficient friction force to urge the feedstock through the extrusion orifice.

Dec. 2, 1975 United States Patent 1191 Voorhes 1 1 EXTRUSION PROCESS 72/60 Green 72/262 Stulen Fuchs...

lnvcntor: William G. Voorhes, East Greenwich, R.l.

[73] Assignce: Wanskuck Company, Providence,

Primary E.\'aminerLowell A. Larson Attorney. Agent. or FirmBarlow & Barlow 22] filed: Mar. 20, 1975 [57] ABSTRACT A process and apparatus for extruding feedstock in which the gripping force for extrusion of the feedstock Appl. No.: 560,182

Related US. Application Data 56,354. March 29 is derived by forcing the feedstock into a passageway to develop in the feedstock on two opposing surfaces 1974. abandoned.

a pressure of at least the yield strength of the feedstock and moving the opposed walls of the passageway toward an end wall with extrusion orifice means located at or near the end wall of the passageway where 00 w m UB3 2H3 7 C m n M B 2 7 m 4 u 2 u 7 u r a C O t U .m N H 5 5 [58] Field of Search....,.......... 72/41 additional constraining walls are provided at least as long as the upset length of the feedstock so as to re- [56] References Cited strain the same within the passageway. the engage- UNITED STATES PATENTS ment of the feedstock between the moving walls creating sufficient friction force to urge the feedstock through the extrusion orifice.

425/376 6 Claims, 11 Drawing Figures Bimba ct Upton F L33 555 999 HHH 76 807 3007- 227 045 $7.7.

U.S. Patent Dec. 2 1975 Sheet 1 of 3 3,922,898

Sheet 2 of 3 3,922,898

US. Patent Dec. 2, 1975 FIG.5

EXTRUSION PROCESS CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my earlier filed application Ser. No. 456,354, filed Mar. 29, 1974, now abandoned.

BACKGROUND OF THE INVENTION i Conventional extrusion involves the placing of a billet into a container which has a die at one end thereof and then with a ram applying pressure to the billet such that the billet is coined into the container by the ram and sufficient force exists to force the billet forward to the die and cxtrude metal therethrough. Recent developments have been directed toward finding a means for continuously extruding. The earliest development utilizes viscous drag of a flowing liquid to feed the feedstock to the die where normal hydrostatic conditions operate in the extrusion zone, and this is disclosed in the Fuchs US. Pat. 3,667,267 of June 6, 1972. A successor to this method also developed by Fuchs is one in which the motion to the rod is transmitted by shear forces developed between a highly viscous fluid coating on the rod and a moving endless pressure chamber that grips the rod on four sides as disclosed in US. Pat. 3,740,985 of June 26, 1973. A still further development utilizes mechanical friction to feed the feedstock toward the die and provide the necessary pressure for extrusion to occur as disclosed in Green patent US. Pat. No. 3,765,2l6 of Oct. 16, 1973. In the Green system, the feedstock has an interference fit in the groove or passageway in order to set up frictional forces, there being three moving sides and one stationary side. The compressive stress is low where the feedstock enters the passageway, the feedstock being gripped only by compression of some outer fibers. As the feedstock approaches the die, the compressive stress increases until it exceeds the yield strength of the feedstock, causing the feedstock to yield and upset, completely filling the passageway along a portion of its length immediately preceding the die.

SUMMARY OF THE INVENTION The main object of this invention is to provide an improved apparatus and method for applying substantial gripping pressure throughout the length of the passageway at least as high as the yield strength of the feedstock material on two opposed sides of the feedstock material and to continuously and steadily advance the feedstock through an extrusion die located at or near the end of a passageway.

This invention relates to the discovery of the fact that two-sided gripping may be utilized in continuous extrusion provided that lubrication is applied to the ungripped surfaces before they upset against the additional constraining walls located at the end of the passageway. Two-sided gripping of the feedstock consists of taking a continuous length of feedstock and compressing it on two opposing sides until the feedstock is deformed plastically to a point beyond the yield strength of the feedstock material into substantially rectangular cross section. Conventional gripping of the feedstock material as has been accomplished in the prior art mentioned in the Background of Invention paragraph does not achieve the degree of compression of the feedstock that is achievedby the instant invention nor does it operate with only two surfaces gripping.

For example, if one wishes to consider the various factors involved, it can be demonstrated that utilizing the method and apparatus disclosed in the Green patent referenced above and comparing it with the apparatus of the instant invention that approximately a 30% reduction in power required to perform extrusion can be achieved using the instant invention. These figures, of course, are related to two systems having identical parameters.

In practicing the extrusion in accordance with the present invention, feedstock is forced into a passageway so as to compress two opposing surfaces thereof to a point at least to the pressure of the yield strength of the material. The two opposed walls of the passageway are moved toward an end wall having a die means at or near thereto which is provided with another pair of opposed walls of a length in excess of the upset length of the material of the feedstock, which upset length is the distance from the extrusion orifice up to the point at which upsetting of the feedstock occurs, this length being easily calculable since it is known that this yielding or upsetting of the feedstock and the length over which this occurs can be determined by a formula wherein it is dependent upon such factors as the pressure of extrusion, the width and depth of the passageway, and the yield strength of the feedstock. As the feedstock approaches the end wall, the other surfaces of the feedstock not already gripped will upset against these constraining walls and the extrusion action will occur due to the fact that sufficient force is available for continually moving the feedstock and extruding the same through the extrusion orifice.

Briefly, therefore, the present invention consists of the steps of forcing feedstock into a passageway to plastically deform the feedstock against two opposing surfaces of the passageway to a point where a pressure is achieved in the feedstock of at least the yield strength of the feedstock, this pressure being achieved against two opposing walls of the passageway and moving these two opposing walls towards an end wall at the end of the passageway and providing adjacent to the end wall constraining walls, the feedstock upsetting against these constraining walls, and the two first opposing surfaces advancing the feedstock through an extrusion orifice.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 represents a detached perspective view of a basic form of apparatus for practicing the present invention;

FIG. 2 is a perspective view partially diagrammatic illustrating the principle of the present invention;

FIG. 3 is a perspective view representing another form of apparatus for practicing the present invention;

FIG. 4 is a sectional view taken on lines 44 of FIG.

FIG. 5 is a partial enlarged central vertical sectional view of the apparatus of FIG. 3;

FIG. 6 is a plan view of another form of fork;

FIG. 7 is a perspective view partly broken away showing a still further form of apparatus for practicing the present invention;

FIG. 8 is a longitudinal sectional view of the device of FIG. 7;

FIG. 9 is a perspective view partly broken away showing another form of apparatus;

FIG. 10 is a transverse sectional view of the central portion of the apparatus of FIG. 9; and

FIG. 11 is a sectional view of line ll-ll of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENT generally designated 18, which fork has a pair of legs 0 20 and 22 which respectively have opposing walls 24 and 26. A die insert 28 is located at one end of the legs 22, 20 and has an orifice 29 therein of a shape of the product to be extruded, said die insert being restrained from forward motion by an end wall which is the base of the fork 18. In this configuration the parts and 12 are clamped together and move relative to the part 18. To understand how this system operates reference should now be made to FIG. 2. Here feedstock F is illustrated as being clamped on two opposed surfaces A and B thereof by the blocks 10' and 12 which exert pressures P as shown by the arrows on the faces A and B, which pressures P are of at least the yield strength of the material of the feedstock F because the initial thickness t of the feedstock before clamping exceeds which is the thickness of the fork and of the feedstock after clamping. Relative motion can now be achieved between the fork l8 and the blocks 10' and 12'. Lubricant is injected into the space between the ungripped surfaces of the feedstock and the legs of the fork through ports 21 and 23, said ports being located upstream of the upset region delineated by I. Let us assume for the sake of discussion that the fork 18 is pushed to the right as viewed in the drawing and the blocks 10' and 12 that are holding the feedstock F remain stationary. As the die face 28 strikes the feedstock F, an axial compressive stress is set up in the feedstock. As the fork moves further to the right, the axial compressive stress increases until it exceeds the yield strength of the feedstock, causing the feedstock material to yield and upset, thereby filling the cross section of the fork delineated by the walls 24, 26 and the surfaces 14 and 16 of the clamping blocks (see FIG. 1). Feedstock now fills the entire cross section in front of the die face and as the fork continues to move to the right, sufficient pressure will develop at the die face for extrusion to occur through the die, the feedstock being restrained along an upset length l as shown in FIG. 2 on the faces 24, 26 of the fork. Sufficient frictional force is available by virtue of the clamping action of the blocks 10 and 12' to withstand the axial force caused by the pressure on the die face.

As explained by Green in his U.S. Pat. No. 3,765,216 and the article in Journal of the Institute of Metals, 1972, Vol. 100, p. 295, the compressive stress on the feedstock in the die region will exceed the yield strength of the feedstock, causing the feedstock to yield and upset completely filling the passageway over a portion of its length immediately preceding the die. The relationship between this upset length I, the groove width W, the pressure P at the die face during extrusion and the yield strength Y can be expressed From Rathke, ASME paper 73 WA/PT -4, 1973, we learn that the pressure profile decreases exponentially along the feedstock in proximity to the die. Accordingly, the average pressure along length 1 may be approximated Now determine the pressure required at the die face for extrusion in a system where two sides of the feedstock are gripped and the ungripped surfaces are free to upset against the legs of a fork. First assume that the thickness of feedstock is t, after the two sides are gripped (see FIG. 2) and that the spacing between the legs of the fork is W. Assume (to simplify the analysis) that t W. Also assume that the feedstock is stationary and the fork is pushed to the right, causing stock to be extruded to the left. The force required to push the fork to the right can be expressed:

(FORCEFURK o FRIITIox) (3) I-URK and therefore But, from equation (1),

P IY/W; upon substituting for P in equation (7), it can be shown that for which the reasonable solution is This equation shows why it is necessary to lubricate the ungripped surfaces. For example, assume that aluminum feedstock is being extruded into a steel fork and the ungripped surfaces are not lubricated. A typical value for [L would be 0.47. Assume also that P,, 3). Upon substituting these values in equation (8) it can be seen that the solution would be imaginary. This means that the upset length I would never stabilize. but would increase continually as the yoke continued to be pushed to the right. Assume now that the ungripped surfaces are lubricated, thereby reducing p. to 0.05.

Upon solving the equation, it can be seen that which means that the system would be stable.

Upon substituting for l in l the pressure at the die face can be seen to be:

The force required for extrusion, being equal to the die face pressure times the die face area, can be seen to be FORCE, 3 7UYW- And since P will equal P,

The force required to overcome friction along length I can be expressed FIHI'TIUX AI'G- so that the total force required for extrusion can be expressed:

/u'rm'xmx u Arlw -I I Upon substituting (9) and (10) in l 1 it can be shown that:

o I Y 3 Assume that P,, 3Y (as before) and that p. 0.47, which is a typical value for aluminum feedstock sliding against a steel shoe. Upon substituting these values into equation it can be seen that EHIWWFS .35 w

As hereby demonstrated, the present invention requires about 30% less force for extrusion than the Green invention. Since power equals extrusion force times feedstock velocity, the present machine requires about 30% less power than the Green invention to extrude feedstock at a given velocity.

Referring now to FIGS. 3, 4 and 5 of the drawings, there is shown an alternate form of'the device which can be used to make the process continuous. This is done most simply by replacing the flat blocks 10 and 12' of FIG. 2 with circular blocks 30 and 31 which rotate about shafts 32 and 33 respectively in the direction of the arrows. A fork 35 of thickness 1, and containing a die insert 36 is positioned between the two rotating blocks and held in position by retaining members 38, 39 which embrace the fork. As seen in FIG. 5, the rotating blocks advance feedstock F on initial thickness t into the fork, thereby reducing feedstock thickness from to t The thickness of the feedstock is such that when the feedstock is compressed to thickness 1 there is developed on the two opposing surfaces contiguous to and gripped by the circular blocks 30, 31 a pressure exceeding the yield strength of the feedstock material. The feedstock is lubricated on the ungripped surfaces through ports 41 and 43. As the blocks rotate,

FORCEHXTRI'SIOX POWIz-I'PUWz the feedstock is forced against the die face 37, the feedstock thereby upsetting over a length I as disclosed in FIG. 4 and extruding through the die insert 36.

FIG. 6 illustrates a variation in fork design which is facilitated by the apparatus of the instant invention. To this end, the fork 45 has a pair of legs 46, 47 and an end wall 48. An extrusion die port 50 is provided in at least one leg and the plasticly deformed feedstock will upset and extrude through the die port 50. As in the other embodiments lubrication ports 51, 52 are provided.

In FIGS. 7 and 8 there is shown a still further arrangement for continuous extrusion embodying the principles of this invention in which the pressure gripping the feedstock and which exceeds the yield strength of the feedstock material is provided by a series of blocks connected together to form endless belts such as 70, 72 which are trained over drive sheaves 74, 76 and idler sheaves 73, and which are urged against the feedstock F by means of two guide forms 78 (only one being shown in FIG. 7) that force the gripping elements into contact with the feedstock F, thereby reducing feedstock thickness from 1 to t,. The drive sheaves 74, 76 rotate in the direction of the arrows, thereby advancing the gripping elements and the feedstock in the direction shown. It is desirable to inject lubricant between each gripping element and its contiguous guide form to reduce frictional drag. In all other respects the operation of this particular embodiment is substantially identical to that disclosed in connection with FIGS. 1 and 2 and includes lubrication ports 21, 23' for injecting lubricant into the space between the ungripped surfaces of the feedstock and the legs of the fork.

Referring to FIGS. 9-11, there is disclosed a further arrangement of a continuous extruder. In this form a pair of blocks 80, 82 are provided with grooves 81, 83. Between the blocks there is positioned a fork member 18" that is similar to fork 18 of FIG. 1 and provides an end wall supporting a die insert 28" and ports 21" and 23" for lubricating the ungripped surfaces of the feedstock. A pair of flexible bands 84, 86 are trained over drive sheaves 89, 91 and idler sheaves 88, and into the grooves 81, 83. The sheaves are driven by means not shown, and move feedstock F as in the direction of arrow 92 toward the die held by the fork. The blocks 80, 82 are clamped against the fork 18" by suitable means, such as bolts 96, to withstand the separating forces developed when the feedstock is compressed beyond its yeild strength. As in FIG. 7, it is desirable to inject lubricant between each band and its contiguous block, for which ports 94 and 95 are provided.

I claim: I

1. A process of continuously forming feedstock comprising the steps of providing a gripping means, gripping two opposed sides of feedstock material whereby the two opposing sides of the material are compressed to a pressure greater than the yield strength of the material, lubricating the ungripped surfaces of the feed stock, providing a fork-shaped element having opposed constraining walls, locating a die means in the vicinity of the base of the fork, moving the feedstock toward the die means by the gripping means, maintaining the gripping force greater than the yield strength of the material throughout the fork-shaped element, whereby as the feedstock is urged against the base of the fork the feedstock upsets against the constraining wall surfaces and passes out through the die means, the gripping means advancing the feedstock into the fork, said gripping means and constraining wall surfaces of said fork forming a passageway.

2. Extrusion apparatus comprising a first gripping means, and a second wall means comprising a forkshaped member having two opposed walls and a base section, said gripping means and said second means being relatively movable, said gripping means operating on two opposed sides of feedstock material, said first and second means defining a passageway, a die means with an orifice positioned between said opposed walls in the vicinity of the base section, and means for moving one of said two means whereby feedstock material is moved toward said die, lubricating means for applying lubricant to the adjacent surfaces of the second means and the feedstock, said gripping means applying a compressive force to the feedstock greater than the yield strength of the feedstock, the gripping means advancing the feedstock through the die and 8 maintaining the gripping force greater than the yield strength of the material throughout the forkshaped member.

3. Extrusion apparatus as in claim 2 wherein said gripping means comprise a pair of bands, said bands being guided for longitudinal movement along a pair of arranged for rotative movement on parallel axes. 

1. A process of continuously forming feedstock comprising the steps of providing a gripping means, gripping two opposed sides of feedstock material whereby the two opposing sides of the material are compressed to a pressure greater than the yield strength of the material, lubricating the ungripped surfaces of the feedstock, providing a fork-shaped element having opposed constraining walls, locating a die means in the vicinity of the base of the fork, moving the feedstock toward the die means by the gripping means, maintaining the gripping force greater than the yield strength of the material throughout the fork-shaped element, whereby as the feedstock is urged against the base of the fork the feedstock upsets against the constraining wall surfaces and passes out through the die means, the gripping means advancing the feedstock into the fork, said gripping means and constraining wall surfaces of said fork forming a passageway.
 2. Extrusion apparatus comprising a first gripping means, and a second wall means comprising a fork-shaped member having two opposed walls and a base section, said gripping means and said second means being relatively movable, said gripping means operating on two opposed sides of feedstock material, said first and second means defining a passageway, a die means with an orifice positioned between said opposed walls in the vicinity of the base section, and means for moving one of said two means whereby feedstock material is moved toward said die, lubricating means for applying lubricant to the adjacent surfaces of the second means and the feedstock, said gripping means applying a compressive force to the feedstock greater than the yield strength of the feedstock, the gripping means advancing the feedstock through the die and maintaining the gripping force greater than the yield strength of the material throughout the fork-shaped member.
 3. Extrusion apparatus as in claim 2 wherein said gripping means comprise a pair of bands, said bands being guided for longitudinal movement along a pair of block-like members.
 4. Extrusion apparatus as in claim 2 wherein said gripping means comprise a pair of blocks.
 5. Extrusion apparatus as in claim 2 wherein the gripping means comprises a series of blocks connected together.
 6. Extrusion apparatus as in claim 2 wherein the gripping means comprises a pair of opposed circular blocks arranged for rotative movement on parallel axes. 